1. Field of the Invention
The present invention relates to a fluid transmission device including a torque converter and a fluid joint which is used in an automobile and the like, and more particularly to an improvement in a fluid transmission device comprising: a turbine impeller; a pump impeller which is opposed to the turbine impeller so as to define a circulation circuit of a working oil between the pump impeller and the turbine impeller, and which has a pump shell including a diameter-expanded portion along a peripheral end portion; and a cylindrical transmission cover which defines an oil chamber in communication with the circulation circuit between the transmission cover and a back surface of the turbine impeller, a male fitting surface of a periphery of the diameter-expanded portion being fitted to a female fitting surface of an inner circumference of a peripheral wall portion of the cylindrical transmission cover, a fillet weld being formed between an end surface of the peripheral wall portion and a peripheral surface of the diameter-expanded portion along an entire circumference thereby connecting together the pump shell and the transmission cover.
2. Description of the Related Art
Such a fluid transmission device has already been disclosed, for example, in Japanese Patent Application Laid-open No. 2004-239365.
In recent years, for such a fluid transmission device, there has been a demand for an increase in load capacity corresponding to the high output of an engine, so that it has become necessary to increase the diameter of a fluid container comprising a pump shell and a transmission cover. However, when the size of the fluid container becomes large, a radial load which acts on the peripheral wall increase greatly due to an increase in centrifugal force and inner pressure, resulting in that excessive stress is likely to concentrate on a weld between the pump shell and the transmission cover. Therefore, it is conceivable to reduce the stress on the weld by increasing the plate thickness of the pump shell and the transmission cover to increase their rigidity. With this arrangement, however, the weight of the fluid container greatly increases, not only increasing the cost, but also lowering performance such as acceleration response.